Enkephalin increases the efficacy of dopaminergic transmission in Helix pomatia.

A dopaminergic synaptic connection in Helix pomatia was studied. Transmitter mobilization was measured during incubation with met-enkephalin. Enkephalin decreased the time constant for transmitter mobilization. The effect was blocked by naloxone. It is postulated that the presynaptic cell possesses opiate receptors and that these receptors mediate the enkephalin-induced increase in efficacy of dopaminergic transmission.